Benny,

4 is a lot in arace to still make a profit.
Basics of Dutch betting:
1. Rank your top selections as contenders e.g. 1 -4
2. Choose your target collect
3. Choose target margin to determine amount to outlay e.g. if collect target is $100 and aim for 100% profit outlay is $50
4. Get odds for selections
5. Work down through your selections to colect $100 if ewach one wins until you have spent $50. Stop there
e.g. if your picks are paying $5, $3, $8, and $10 respectively you will bet $20 on the first pick $32 on the 2nd and that is all to maintain your margin.
If your 2nd and 3rd picks are paying $8 and $10 then you can fit in three by betting $20 on first, $12 on 2nd, $10 on 3rd and still keep your margin over 100%.
Hope this helps.